This invention relates generally to methods of detecting turbulence in air flow and for measuring the velocity of air flow. More specifically, the invention constitutes improvements over the methods disclosed in Schmalz U.S. Pat. No. 4,896,532.
That patent discloses a method in which a tracer gas is introduced into a moving air stream. The tracer gas is a non-toxic gas such as nitrous oxide having a vibrational absorption frequency in the infrared range. A warm background is positioned at one side of the air stream while a filter-equipped infrared camera is positioned at the other side of the stream and is directed toward the warm background. The camera detects the flow pattern of the tracer gas and produces a permanent photographic images, turbulence in the air stream may be visualized and analyzed.
Nitrous oxide is heavier than air and this presents a particular problem when the tracer gas is injected into a horizontally flowing air stream. The heavier tracer gas tends to sink within the stream and does not follow the same trajectory as the stream. Sinking of the tracer gas also presents a problem when the tracer gas is injected into a substantially stationary air mass.
Also, the methods disclosed in the Schmalz patent do not lend themselves to use in applications where it is not possible to place the warm background and the infrared camera on opposite sides of the air stream under study. For example, when studying air stream escaping from leaks in a structure, it is often impossible or impractical to place a warm background directly adjacent the structure.
The Schmalz patent also discloses a method of measuring the velocity of an air stream by injecting pulses of tracer gas into the stream and by using the camera to detect and record parameters relating to the velocity of the stream. The manner in which the tracer gas is injected, however, makes it difficult to obtain in the stream a well-defined pulse whose velocity accurately reflects the velocity of the stream.